Watthour meter shunt assembly



out applying local stresses .or strains thereto.

United States Patent @fifice This invention. relates to magnetic shuntassemblies and it has particular relationto magnetic overload shuntassemblies for watthour meters.

It is well-known in the art that magnetic overload shunts are desirablefor watthourmeters in order to improve the accuracy. of :suchmeters-over a large range of load variations. A conventional magneticshunt assembly for a watthour meter may include a magnetic shunt mem-'ber.which is positioned on a non-magnetic base carrier or spacer.member. These members are secured to each other in a suitable mannersuch as by rivets or bent tabs. Examples of such prior art constructionof magnetic shunt 'assemblies will be found in the. Leippe Patent r2,169,029 and T. .D. Barnes Patent 2,177,274.

In accordancewiththe invention, magnetic shunt membeiis'embeddedentirely orpartly in a suitable moldable material. Althoughthe'moldable material may be of a non-metallic nature such :as aphenolic resin, preferably a diecasting metallic alloy is employed asthe material. A low-melting-point lead-base alloy has been foundparticularly desirable.

During a molding operation, the moldable material flows uniformly overthe magnetic shunt member and engages the magnetic r shunt member over.large areas with- Since dimensions may be maintained accurately inthemoldable material, the shunt member is located accurately with respectto the accompanied carrier member and the absence of local stresses andstrains assures the absence of changes in physical locations as well asmagnetic properties of the shunt assembly.

If desired, the magnetic shunt member may be completely embedded in theassociated carrier member. However, in a preferred embodiment of theinvention, the face of the shunt member is exposed. The molded carriermember preferably has a rim which completely surrounds the periphery ofthe shunt member and protectsit at all times.

The shunt assembly is applied to a watthour meter electromagnet bywedging. it between the current pole pieces of the electromagnet.

The material employed for the carrier member is readily wedged betweenthe pole pieces and engages them to retain the shunt assembly accuratelyin operative position. This is particularly true if the pole pieces are.of laminated construction for the reason that the carrier member tendsto interlock with the laminations of the pole pieces to preventsubsequent displacement of the shunt assembly.

If a moldable material is of a type which wets the surfaces of the shuntmember and adheres thereto, retention of the shunt member by the carriermember is assured. In a preferred embodiment of the invention, the twomembers are interlocked with each other to assure permanent assemblythereof. 'Inasmuchas the shunt member is fully supported by the carriermember, no limitations are imt q sd a the h e and mm r h p et a s ewhen.

Patented N 0v. 12,. 1957 netic shunt assembly wherein a die-castingalloy protects at least two edges. of a magneticshunt.

. It is also. an object of the invention to provide a, mag netic shuntassembly wherein a shunt. member is embed- .ded in a die-castingalloywhich surrounds. at leastthe edges of the magnetic shunt membershunt member.

.Itis an additionalobjectto provide awatthour meter having spaced. polepieces and an improved shunt. as

and one face of the sembly including .a molded carrier member. extendingbe- .tween the pole pieces.

Other objects .ofthe inventionwill be apparentfrom the followingdescription taken in conjunction with the accompanying drawing, inwhich:

Figure 1 is a view in rear elevation of awatthourmeter embodying theinvention;

Fig. 2 .is a view intop plane, with .parts broken away, of a.magneticshuntassembly employed in the watthour member of Fig. 1,together with the associated pole pieces; and

.Fig. 3 is a .view in crosssection of the shunt assembly illustrated inFig. .2 taken along theline III--III andlocated in a mold cavity.

Referring to the drawing of Fig. 1, a watthour meter 1 having. an.electromagnetl 3 and an electro-eonductive armature or disc 5 whichismounted for rotation about its axis relative to theelectr'omagnet 3 isshown.

Thelelectromagnet 3 includes a magneticistructure constructed of softmagnetic material to-prov'ide a voltage .pole piece 7 having a pole face7P and a pair of spaced parallel current pole pieces 9 and 11 havingpole faces 9P and 11F. By inspection of. Fig. .1, it will be noted thatthe pole faces 9P and HP are. disposed in a common plane and arespacedfrom the pole face 7P of the voltage pole pieces to define an airgap 13 in which a portion of the disc 5 is located.

In order to establish a magnetic field in the air gap 13,

' a voltage winding 15 surrounds the voltage pole piece 7 and whenenergized directs magnetic flux through .the pole piece into the airgap. Current windings '17 and 19, respectively, surround the currentpole pieces9 and 111. When the windings 17 and 19 are suitablyenergizeda magnetomotive force is developed between the pole faces 9Pand HP for the purpose of directing magnetic flux .into the air gap '13.The magnetic structure of Fig. 1

conveniently is constructed of a plurality of similar thin laminations L(Fig. 2) which are secured to each other by means of rivets 21 passingthrough the laminations in a direction transverse to the planes of thelaminations. Inasmuch as watthour meters are well-known in the art, amore detailed discussion of the electromagnet of Fig. 1

and its operation is unnecessary.

As shown in Fig. 1, the pole pieces 9 and 11 have lips 9L and 11L whichproject from the pole pieces toward each other adjacent the polepieces9P and 111. Portions of the lips are undercut to define retaining ledges9E and 11E for the purpose of retaining therebetween a shunt assembly.The shunt assembly has a protuberance 25 which projects intothe spacebetween the lips 9L and 11L.

.As shown in Figs. 2 and 3, the shunt assembly 23 includes a'magneticshunt sequently shunts a substantial percentage of the magnetic fluxproduced by these windings away from the air gap. As the energization ofthese windings increases, the shunt begins to saturate and as itsaturates, a smaller proportion of the magnetic flux produced by thewindings 17 and 19 is shunted away from the air gap. This compensatesfor the well-known tendency of the watthour meter to operate too slowlyat larger encrgizations of the current windings. As well understood inthe art, the term saturated is employed to refer to decrementalpermeability or effective decrease in permeability or relatively fastreduction in permeability, of the magnetic shunt. By proper selection ofthe proportions of the magnetic shunt the rotation of the disc.5 can besubstantially proportional to the power measured by the watthour meterover a large range of variations of power.

As previously pointed out, the carrier member 29 preferably isconstructed of a moldable'material. In a preferred embodiment of theinvention, the moldable material is a die-casting alloy. If the magneticshunt member 27 is constructed of a cold-rolled steel which is properlycleaned and fiuxed if necessary, the moldable material employed for thecarrier member may be selected to wet the surface of the shunt memberand adhere directly, thereto.

As previously pointed out, the preferred moldable material is alead-base material containing more than 50% lead. As a specific exampleof such a material, the carrier member may be constructed of adie-casting alloy containing 78% to 81% lead, 14% to 16% antimony, and4% to 6% tin, by weight. However, the constituents may vary appreciablyfrom these proportions with good results.

The moldable material may be applied to the magnetic shunt member 27 inasuitably shaped cavity of a mold 31' having a base 31B and a cover 31C.The shunt member 27 is positioned in any suitable manner as on pins 33which project into the cavity of the mold from the base 31B. One ofthese openings is provided adjacent each corner of the shunt member.When the shunt member is withdrawn from the mold four holes 35, 37, 39and 41 are left in the carrier member. Transverse movement of the shuntmember in the mold may be prevented, if necessary, in any suitable wayas by providing the member with shallow recesses for receiving the pins33.

Although the shunt member could be completely embedded in the moldablematerial, preferably the upper face of the shunt member is left exposed.As shown in Fig. 3, the upper face of the shunt member 27 ismaintainedin engagement with the adjacent wall of the mold 31.

To assure retention of the shunt member 27 by the carrier member 29,-interlocking maybe provided between the members.

engaging the ledges 9E and 11B of the current pole pieces. lnorder tofacilitate insertion of the magnetic shunt assembly between the polepieces, the bevels 47 and 49 may be made shomewhat deeper adjacent theirends to provide somewhat thinner leading edges of the shunt assembly forinsertion between the pole pieces. However, the main body of the shuntassembly isslightly longer than thedistance between the ledges 9E and11E to provide a press fit. Consequently, the shunt assembly isfirmlywedged into afinal position.

Because of the material employed a secure interlocking is providedbetween the carrier member and the Two counter-sunk holes 43 and 45 areformed in the shuntmember 27. During the moldinvention are possible.

4 laminations of the pole pieces. Consequently, following installationof the shunt assembly, accidental displacement thereof does not occur.

The rigidity of the shunt assembly is increased by providing theprojection 25 adjacent the central part of the shunt assembly. Thisprojection also improves the flow of the moldable material which isinserted into the mold cavity through a suitable sprue 51.

The lead-base die-casting alloy has a low melting point and isintroduced into the mold cavity in a very fluid condition underpressure. The material flows uniformly around the shunt member withoutsubjecting the shunt member to local stresses. Shortly after theintroduction of the moldable material, the pressure is relieved and thestill fluid material in the sprue 51 drops away from the part in therestricted cross-section of the sprue which is the first to solidify.However, it will be understood that other molding or casting techniquesmay be employed if so desired. Following the cooling and solidificationof the assembly, the cover 31C is removed from the base 31B and theshunt assembly is completely withdrawn from the mold.

It will be noted further by inspection of Figs. 2 and 3, that thecarrier member provides a rim completely surrounding the periphery ofthe magnetic shunt member 27. Thus adequate protection is providedagainst bending or other injury to the magnetic shunt member. If themoldable material is of a type that adheres firmly to the shunt member,it also provides good protection against corrosion of the shunt member.

Although the invention has been described with reference to specificembodiments, therefore, numerous modifications falling Within the spiritand scope of the Consequently, the illustrations in the drawing and thedescription herein presented are to be construed in an illustrativerather than a limiting sense.

I claim as my invention: 1

1. In a watthour meter, an electromagnet comprising a pair of spacedmagnetic current pole pieces having pole faces substantially in a commonplane and a magnetic voltage pole piece having a pole face spaced fromthe plane to define an air gap therebetween, current winding meansassociated with the current pole pieces for establishing, whenenergized, a magnetomotive force between the pole faces of the currentpole pieces, and voltage winding means for directing, when energized,magnetic flux through the voltage pole piece, in combination with ashunt assembly disposed between the current pole pieces adjacent saidplane for shunting magnetic flux pro-- duced by the current windingmeans away from said air gap, said shunt assembly comprising a. magneticshunt member extending substantially between .the currentpole pieces anddesigned to saturate within the range of said magnetomotive force forwhich the electromagnet is designed, and a carrier member wedged betweenthe current pole pieces, said carrier member having acavity proportionedto receive snugly the shunt member, said carrier member and the shuntmember having uniform surface engagement throughout substantial engagingsurfaces, said carrier member comprising a die-casting alloy molded inintimate engagement with the shunt member, said carrier member engagingsaid current pole .pieces to space the shunt member fromthe pole pieces.

2. In a watthour meter, an electromagnet comprising a pair of spacedlaminated magnetic current pole pieces having pole faces substantiallyina common plane and a magnetic voltagepole piece having a poleface spacedfrom the plane todefine an air gap therebetween, current winding meansassociated with the current pole pieces for establishing, whenenergized, a magnetomotive force between the pole faces of the currentpole pieces, and voltage Winding means for directing, when energized,magnetic through the voltage pole piece, in combination Wlll'l a shuntassembly disposed between the current pole pieces for shunting magneticflux produced by the current winding means away from said air gap, saidshunt assembly comprising a magnetic shunt member extendingsubstantially between the current pole pieces and designed to saturatewithin the range of said magneto motive force for which theelectromagnet is designed, and a carrier member wedged between thecurrent pole pieces, said carrier member comprising a uniform diecastingmaterial embedding and intimately engaging a substantial portion of theshunt member and engaging the edges of the laminations of the currentpole pieces.

3. In a watthour meter, an electromagnet comprising a pair of spacedmagnetic current pole pieces having pole faces substantially in a commonplane and a magnetic voltage pole piece having a pole face spaced fromthe plane to define an air gap therebetween, current winding meansassociated with the current pole pieces for establishing, whenenergized, a magnetomotive force between the pole faces of the currentpole pieces, and voltage winding means for directing, when energized,magnetic flux through the voltage pole piece, in combination with ashunt assembly disposed between the current pole pieces for shuntingmagnetic flux produced by the current Winding means away from said airgap, said shunt assembly comprising a magnetic shunt member extendingsubstantially between the current pole pieces and designed to saturateWithin the range of said magnetomotive force for which the electromagnetis designed, and a carrier member held by engagement with the currentpole pieces, said carrier member comprising a uniform die-casting metalalloy molded around one face and the sides of the shunt member toprovide a rim surrounding the shunt member.

4. In a watthour meter, an electromagnet comprising a pair of spacedmagnetic current pole pieces having pole faces substantially in a commonplane and each having a lip adjacent said plane, said lips projecting indirections towards each other, the free ends of the lips being spacedfrom each other, said pole pieces comprising laminations each transverseto the plane and parallel to said directions, and a magnetic voltagepole piece having a pole face spaced from the plane to define an air gaptherebetween, current winding means associated with the current polepieces for establishing, when energized, a magnetomotive force betweenthe pole faces of the current pole pieces, and voltage winding means fordirecting, when energized, magnetic flux through the voltage pole piece,in combination with a shunt assembly disposed between the current polepieces for shunting magnetic flux produced by the current winding meansaway from said air gap, said shunt assembly comprising a magnetic shuntmember extending substantially between the current pole pieces adjacentthe pole faces thereof and designed to saturate within the range of saidmagnetomotive force for which the electromagnet is designed, and acarrier member wedged between the current pole pieces, said carriermember engaging said lips and having a portion extending between thelips, said carrier member comprising a die-casting material embedding asubstantial portion of the shunt member, said shunt member having anexposed face defining a portion of said air gap.

5. An electromagnet comprising a magnetic structure having pole pieces,said pole pieces having pole faces defining an air gap, winding meanseffective when energized for establishing a magnetomotive force betweensaid pole faces to produce a magnetic field in the air gap, and amagnetic shunt assembly disposed to shunt magnetic flux produced by saidmagnetomotive force away from the air gap, said magnetic shunt assemblycomprising a magnetic shunt member positioned to carry magnetic fluxproduced by the magnetomotive force and proportioned to saturate withinthe range of energization of the winding means, and a carrier membersubstantially embedding the shunt member, said carrier member comprisinga die-casting metal alloy molded about said shunt: member and abuttingsaid pole pieces, said carrier member spacing said shunt member from thepole pieces. 1

References Cited in the file of this patent UNITED STATES PATENTS312,485 Makin Feb. 17, 1885 2,177,274 Barnes Oct. 24, 1939 2,501,535Nobbs Mar. 21, 1950

